Phenazine-Producing Rhizobacteria Promote Plant Growth and Reduce Redox and Osmotic Stress in Wheat Seedlings Under Saline Conditions

Abstract

Application of plant growth promoting bacteria may induce plant salt stress tolerance, however the underpinning microbial and plant mechanisms remain poorly understood. In the present study, the specific role of phenazine production by rhizosphere-colonizing Pseudomonas in mediating the inhibitory effects of salinity on wheat seed germination and seedling growth in four different varieties was investigated using Pseudomonas chlororaphis 30-84 (wild type) and isogenic derivatives deficient or enhanced in phenazine production. The results showed that varieties differed in how they responded to the salt stress treatment and the benefits derived from colonization by P. chlororaphis 30-84. In all varieties, the salt stress treatment significantly reduced seed germination, and in seedlings, reduced relative water content, increased reactive oxygen species (ROS) levels in leaves, and in three of four varieties, reduced shoot and root production compared to the no salt stress treatment. Inoculation of seeds with Pseudomonas chlororaphis 30-84 wild type or derivatives promoted salt-stress tolerance in seedlings of the four commercial winter wheat varieties tested, but the salt-stress tolerance phenotype was not entirely due to phenazine production. For example, all P. chlororaphis derivatives (including the phenazine-producing mutant) significantly improved relative water content in two varieties, Iba and CV 1, for which the salt stress treatment had a large impact. Importantly, all P. chlororaphis derivatives enabled the salt inhibited wheat varieties studied to maintain above ground productivity in saline conditions. However, only phenazine-producing derivatives enhanced the shoot or root growth of seedlings of all varieties under nonsaline conditions. Notably, ROS accumulation was reduced, and antioxidant enzyme (catalase) activity enhanced in the leaves of seedlings grown in saline conditions that were seed-treated with phenazine-producing P. chlororaphis derivatives as compared to noninoculated seedlings. The results demonstrate the capacity of P. chlororaphis to improve salt tolerance in wheat seedlings by promoting plant growth and reducing osmotic stress and a role for bacterial phenazine production in reducing redox stress.

Interplay between Ca2+/Calmodulin-Mediated Signaling and AtSR1/CAMTA3 during Increased Temperature Resulting in Compromised Immune Response in Plants

“…Results were analyzed using Microsoft Excel. Error bars in all of the figures represent standard error [81]. Number of replicates is described in the figure legends.…”

Rhizosphere plant-microbe interactions under water stress

“…in response to limited soil moisture and over a wide area of the IPNW suggests that dryland wheat gains benefits other than plant defense from these rhizobacteria. To address this possibility, Yuan, Pan, Boak, Pierson, and Pierson (2020) challenged wheat treated with another phenazine producer, P. chlororaphis 30-84, under osmotic stress or water replete conditions. Seedlings colonized with strain 30-84 or its phenazine-deficient and phenazine-overproducing mutant variants exhibited growth promotion under water-replete conditions, but under salt stress, the effect was dependent on the wheat variety and the capacity of the bacteria to produce phenazines.…”

Calmodulin‐binding transcription activator AtSR1/CAMTA3 fine‐tunes plant immune response by transcriptional regulation of the salicylate receptor NPR1

“…Results were analysed using Microsoft Excel. Error bars in all of the figures represent standard deviations (Yuan, Pan, Boak, Pierson, & Pierson, 2020). Number of replicates is described in the figure legends.…”